Becky Oskin writes at LiveScience:
One of Oklahoma’s biggest man-made earthquakes, caused by fracking-linked wastewater injection, triggered an earthquake cascade that led to the damaging magnitude-5.7 Prague quake that struck on Nov. 6, 2011, a new study confirms.
The findings suggest that even small man-made earthquakes, such as those of just a magnitude 1 or magnitude 2, can trigger damaging quakes, said study co-author Elizabeth Cochran, a seismologist with the U.S. Geological Survey.
“Even if wastewater injection only directly affects a low-hazard fault, those smaller events could trigger an event on a larger fault nearby,” she told Live Science.
The Prague earthquake was the largest of thousands of quakes that rattled Oklahoma in late 2011. Three were magnitude-5 or stronger. The 2011 quakes struck along the Wilzetta fault, a fault zone near Prague. Earthquakes break faults like a boat plowing through thick ice — the fault zips open as the earthquake ruptures the fault, and then seals itself shut behind.